1. Field of Invention
This invention relates to resin bonded sand molds and in particular to a system and process for reducing casting pollution, recovering a portion of the molding sand for immediate reuse, producing a low BTU gas fuel by partial combustion of the bonding resin, and recovering a portion of the casting heat.
2. Description of the Prior Art
Heretofore, current foundry practice employing no-bake molds and cores have separate ventilation and sand reclamation operations. Organic waste products are removed from molds and cores in dry scrubbers and transported to dumping sites for disposal; the scrubbed sand is returned for reuse. At the present time there is no practical use for recovered binder residues. Care must be exercised in disposing of the organic waste products, since they pose a potential problem for the environment.
Present ventilation systems include the dilution of foundry air with large quantities of unpolluted air and removing the same from the foundry by forced air and/or induced air systems. The air removed from the foundry is exhausted into the outside atmosphere where air standards are still lenient enough to permit such operation. The existing systems must move huge quantities of air and are therefore expensive to install and maintain operation thereof. Additionally, extra fuel is required to preheat the make-up air for the foundry operation.
Under normal foundry practice, large quantities of silica dust can be present in the foundry environment. This is particularly true in the areas devoted to pouring and shakeout operations. As stated in a volume of American Society for Metal's Handbook, silica dust can produce silicosis if there is sufficient exposure, in terms of time and concentration, to free crystalline silica dust of particle size below five microns. When silica dust concentrations greatly exceed the maximal allowable, a case of silicosis can develop within two to twenty years, the average being ten years.
In no-bake molding practices employing organic foundry sand binders environmental effects must be considered for products of the thermal decomposition of the organic binders. The smoke and thermal decomposition products require control equipment. Thermal decomposition products include, but are not limited to, carbon monoxide, carbon dioxide, nitrogen, hydrogen, methane, formaldehyde, ammonia, hydrogen cyanide, acetylene, ethane, paraffin hydrocarbons, aromatic organic compounds, and the like.
The three major sand reclamation systems currently available to foundrymen using no-bake sands are thermal, wet and dry scrubbing. Thermal reclamation is the most expensive system to install and operate, but produces the cleanest reclaimed sand. A thermal reclaimer requires in the order of 1.5 million BTU's of heat per ton of sand, or 4.5 million BTU's per ton of metal cast, at 3:1 sand to metal ratio to remove up to 96 percent of organic binder residues from any organic no-bake sand mold system. The thermal reclamation system is seldom employed in the industry.
A wet reclamation system is less expensive to operate than a thermal reclamation system, but more expensive than a dry scrubbing system. A wet reclamation system will remove from 35 percent to 45 percent of the organic binder residue from the used no-bake molding sand system. However, the sludge byproduct of the wet reclamation operation requires an environmental safe disposal site.
A dry scrubber system is the least efficient system to reclaim used no-bake foundry sand, its efficiency being of the order of removal of from 25 percent to 35 percent of the binder residues from the sand processed for a shotblast type dry scrubber. This process is employed most often because of its low cost installation.
In the dry scrubber system of reclamation, the sand is crushed and its surface abraded resulting in up to 20 percent of the sand processed being lost because of "dust losses". The wet reclamation system has a less severe "dust loss" process and the thermal system has the least "dust loss" problem.
The binder residues removed by the sand reclamation system have no practical use at this time and their disposal method is dumping.
An object of this invention is to provide a new and improved system and process for casting metals in no-bake sand molds.
Another object of this invention is to provide a new and improved apparatus and process for reducing air pollution in foundries employing no-bake sand molds.
A further object of this invention is to provide a new and improved apparatus and process for causing air to flow through selected regions of a no-bake sand mold to thermally decompose the organic binder therein to produce a gas having a low BTU content.
A still further object of this invention is to provide a new and improved system for insitu thermal recovery of sand from a no-bake sand mold, producing a gas therefrom that has a low BTU content which is storable or can be utilized in several ways for preheating air, and water, for providing heat as required in the foundry.
Another object of this invention is to recover the casting heat from the casting during the cooling cycle.